The present invention is directed to a sensor for monitoring brake wear, particularly in automotive vehicles.
It is a general object of the present invention to provide a simple and inexpensive sensor for monitoring brake wear, either drum-type or disc-type brake wear, in an automotive vehicle environment.
A brake wear sensor in accordance with the present invention includes a body mounting a pair of electrically conductive plates at positions spaced from each other and with each plate having an edge adjacent to a surface of the body. The body includes facility for mounting the body to a brake pad so as to bring the surface of the body, adjacent to which the plate edges are disposed, into position for wearing contact with a brake rotor. Electrical leads and contacts provide for electrical connection to circuitry for monitoring brake wear as a function of changes in capacitance between the plates. That is, the edges of the sensor plates and the surface of the body wear simultaneously with wear at the braking surface of the brake pad, so that changes in electrical capacitance between the sensor plates provide a direct indication of brake pad wear.
In the preferred embodiment of the invention, the body is of insulating material and has an external thread that is adapted to be received within an internally threaded opening in a brake pad to position the wear surface of the body adjacent to the braking surface of the brake pad. In alternative embodiments of the invention, the sensor plates may comprise either flat parallel plates or concentric spiral plates spaced from each other by insulating material. This insulating material may comprise a portion of the insulating body molded between the plates, or separate dielectric material positioned between the plates prior to molding the plates into the body.
Electrical circuitry is connected to the sensor plates for monitoring brake wear as a function of changes in capacitance between the plates. In various embodiments of the invention, this electrical circuitry may include a capacitance bridge in which the plates are connected as one arm of the bridge, a variable frequency oscillator in which the plates are connected as a frequency control component of the oscillator, or an oscillator having an output coupled to the plates such that voltage drop across the plates varies as a function of capacitance between the plates. In the preferred embodiments, at least a portion of the electrical circuitry is disposed in the body of the sensor, preferably by being molded into the body of the sensor simultaneously with the plates. A dashboard gauge may be connected to the electrical circuitry for providing a continuous indication of brake wear to a vehicle operator.